A large portion of automotive assembly involves thin walled material such as sheet metal and plastic. These thin walled components are very flexible and their shape deforms easily when handled. During the inspection process, to check if the parts are in the correct shape and may be used for assembly, physical holding fixtures are created to constrain the parts. Physical holding fixtures are also created to check groups of adjacent parts with regard to how well the parts fit together and to troubleshoot assembly problems.
Sometimes the holding fixtures also model the adjacent thin walled components using precision machined surfaces in order to check critical components in isolation. These inspection holding fixtures are sometimes referred to as Meisterbock, checking fixtures, Total Assembly Checker (TAC) among other names. The fixtures are designed to hold an individual part or sub assembly (like a door) in a constrained and repeatable position simulating how the part will be oriented on the assembled vehicle.
While the current state of the art has been used successfully for many years, there are some limitations. These checking fixtures are expensive to produce. Usually there are long lead times associated with manufacturing these fixtures and this adds to the total time it takes to get a new vehicle into production. These fixtures also tend to be large and take up valuable floor space in the assembly factory. While they aim to be high in accuracy there are always some errors introduced by imperfectly constraining the part due to manufacturing errors in the production of the fixture.
There is another limitation of the current technology in that sheet metal parts are produced by suppliers all over the world. These parts must be shipped to the assembly factory to be checked. When there are defects found, the parts are returned to the supplier along with detailed information regarding the defects, so corrections may be made. Sometimes the parts are not returned but only the corrective data. The logistics of shipping parts back and forth during the pre-production stages often may add to delays in the entry into full production.
In addition, fixtures are static and may only hold the part as they were designed to do. Sometimes flexibility is needed to look at alternate ways of constraining the part in order to solve manufacturing problems. Further, fixtures are not easily or quickly adjustable, for example in order to simulate a systematic production error within a vehicle body (whom the fixture is representing).